Fuel vapour purging systems are generally known and used in different types of vehicles. Fuel vapours are collected and stored temporarily in a canister during periods of a vehicle being in-operative. The vapours are selectively directed to the combustion chamber for burning when the engine is running by drawing air from the atmosphere through the canister, which is referred to as purge operation.
A typical layout of fuel vapour purging system for turbo charged engines comprises of a T-joint, two check valves and a purge valve, which can be operated in duty cycle mode, supplements purge flow under any operating conditions of the engine. Purge systems of this kind with two discharge points (one into the intake manifold, the other to the low-pressure side of the compressor) are commonly known as dual purge systems.
Dual purge systems typically use two check valves. During a first mode of operation, vacuum pressure places the first check valve in an open position and the second check valve in a closed position. In a second mode of operation, pressurized air places the first check valve in a closed position. The second check valve is placed in an open position by vacuum pressure coming either from the pressure sink in front of the compressor stage of the turbocharger or from an additional device like an ejector using a sonic nozzle which converts boosted air into vacuum pressure.
The technical challenge of fitting the purge systems is typically balancing the purging during idle speed (without turbo boost) and above idle speed (engaging turbo booster) i.e. Canister purge valves in general have to fulfil two requirements: low flow operation with high precision metering in normally aspirated mode and high flow capability with low flow restrictions in boost mode. Both requirements are difficult to combine in one valve as the requirements are diverging.
During idle speed and away from turbo boost normally aspirated mode prevails. Fuel vapours are purged from the canister by utilizing the intake manifold's vacuum pressure to draw air through the canister. Typically, during this mode the vacuum pressure is on such a high level, that a very precise metering of the purge valve is required to prevent the engine from running rich in case of purging with a too high flow rate. This precise metering is achieved by running the purge valve in duty cycle mode driven by a PWM-signal.
At above idle speeds while turbo boost is/are engaged, there is no vacuum in the intake manifold to draw air through the canister. The vacuum pressure is created in before the compressor stage of the turbo, which is utilized as the driving force for the purging operation, however the pressure created is very low. Therefore, to provide secure purging from the canister under such conditions, any pressure loss in the purge line needs to be minimized.
The state of the art solution provides additional applications by using additional devices like an ejector using a sonic nozzle, which converts boosted air into vacuum pressure, so that air can be drawn through the canister to purge fuel vapours therefrom. Other solutions include using a dual path dual purge valve system consisting of two different valves. The first valve for normally aspirated mode is a small valve, which enables low flow operation with high precision metering during valve opening; and implementing the second valve for boost mode is a valve with very low flow restriction to be operated in On/Off mode with a sonic Laval-nozzle. The flow behaviour especially at low-pressure gradients, which are available during boost mode in front of the compressor (10 kPa), can be boosted up by using a sonic Laval-nozzle. The requirement for this valve is to allow a high mass flow at low-pressure gradient. In boost mode, the high flow valve has to open a large pressure-impacted cross section, which requires high magnetic forces. However, due to the pressure-impacted across section the best performance is compromised thereby limiting the force available from the solenoid used in the purge valve. Thus, classic high flow valves cannot give the best performance at low-pressure gradients as required.
The closest prior art include examples the use of the low flow valve as a pilot valve for the high flow valve:
US20080290306A1 suggests concept to be applied to a purge valve for purging evaporated fuel stored in a canister to an intake pipe of an engine. The purge valve has a fluid passage connecting an inlet port and an outlet port, and a normally closed valve port that is selectively opened by operation of an electromagnetic actuator is disposed in the fluid passage. A barrier pillar is disposed in the fluid passage between the inlet port and the valve port to suppress transmission of pulsating waves generated in the purge valve to the canister. Flow resistance of the barrier pillar is higher in a reverse flow direction from the valve port to the inlet port than in a normal flow direction from the inlet port to the valve port. The transmission of the pulsating waves is well suppressed by the barrier pillar while allowing a smooth flow from the canister into the purge valve.
U.S. Pat. No. 5,720,469A teaches a two-port electromagnetic valve. The electromagnetic valve incorporates a first port, a second port and a passage for communicating the first and second ports and a cylindrical bobbin having an electrical coil. A fixed core is arranged inside the cylindrical bobbin and has an inner space defined therein. A movable core is arranged near the fixed core. A valve is connected with the movable core for opening and closing the passage between both the ports. An insert member is arranged into the inner space of the fixed core.
US20060243939A1 describes an electromagnetic valve which generally has a housing, a valve element, an electromagnetic driving portion and a filter. The housing forms a fluid flow passage therein. The valve element is installed in the housing to control a flow of a fluid through the fluid flow passage. The electromagnetic driving portion is installed in the housing to generate a magnetic attraction force when it is energized to actuate the valve element. At least a part of the electromagnetic coil is within the fluid flow passage. The filter is installed in the fluid flow passage on an upstream side of the at least a part of the electromagnetic driving portion to filtrate the fluid flowing through the fluid flow passage.
Therefore, in view of the drawbacks highlighted, the present invention provides a dual path dual purging system and valve assembly for turbo boosted engines having two different valve functions into one.